2-emitting radionuclides used for diagnostic (positron emission tomography, PET) and therapeutic (radionuclide therapy in cancer) purposes are typically energetic enough to produce Cerenkov light subsequent to their radioactive decay in tissue. We demonstrate that the light levels produced by these 2- particles are sufficient for external detection of these radionuclides in a mouse using a sensitive charge- coupled device (CCD) camera, thus enabling the distribution of 2-emitting radionuclides to be imaged in vivo using widely available optical imaging systems. We propose to further characterize and optimize the use of Cerenkov light for in vivo small animal molecular imaging, especially for applications involving radionuclide therapies to treat cancer. We also will show how Cerenkov imaging can be used to image the distribution of PET radiotracers using an optical imaging system. Studies will focus on three radionuclides, 18F (a pure 2+ emitter), 90Y (a pure 2- emitter) and 131I (emits both 2--particles and gamma rays). Both 90Y and 131I are clinically used as therapeutic radionuclides. We also propose to develop 3-dimensional Cerenkov luminescence tomography, and show that this has a close relationship to standard bioluminescence tomography. The significance of this work is that for the first time, it allows the distribution of pure 2-emitting radionuclides such as 90Y to be imaged sensitively in vivo, and it also permits the imaging of positron-emitting radiotracers on simple, and widely available optical imaging systems. We think imaging of Cerenkov light will be a powerful new imaging methodology for preclinical molecular imaging and therapeutic studies, and may have certain clinical applications for monitoring therapies involving 2-emitting radionuclides where the target sites can be accessed endoscopically. PUBLIC HEALTH RELEVANCE: 2-emitting radionuclides used for diagnostic (positron emission tomography) and therapeutic (radionuclide therapy in cancer) purposes produce Cerenkov light subsequent to their radioactive decay in tissue. We demonstrate that the light levels are sufficient for external detection using a sensitive charge-coupled device (CCD) camera, thus enabling the distribution of these radionuclides to be imaged using widely available optical imaging systems. The significance of this discovery is that it allows the distribution of pure 2-emitting radionuclides, such as 90Y, to be imaged sensitively in vivo, and it also permits the imaging of positron-emitting radiotracers on simple optical imaging systems.